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| United States Patent |
5,610,223
|
|
Mason
|
March 11, 1997
|
Impact modified polyamide-based molding composition
Abstract
The impact strength of a thermoplastic molding composition containing
polyamide resin is improved upon the incorporation therewith of a
particular silicone rubber powder. The silicone rubber powder, added at a
level of about 1 to 25 percent contains a mixture of (a) a
polydiorganosiloxane and (b) finely divided silica filler.
| Inventors:
|
Mason; James P. (McKees Rocks, PA)
|
| Assignee:
|
Bayer Corporation (Pittsburgh, PA)
|
| Appl. No.:
|
501911 |
| Filed:
|
July 13, 1995 |
| Current U.S. Class: |
524/504; 525/66; 525/474 |
| Intern'l Class: |
C08F 283/12; C08L 083/05 |
| Field of Search: |
524/504
525/66,474
|
References Cited
U.S. Patent Documents
| 3668274 | Jun., 1972 | Owens et al. | 260/857.
|
| 4167505 | Sep., 1979 | Dunkelberger | 260/37.
|
| 4174358 | Nov., 1979 | Epstein | 525/183.
|
| 4221879 | Sep., 1980 | Humme et al. | 525/66.
|
| 4584344 | Apr., 1986 | Baer | 525/66.
|
| 4714739 | Dec., 1987 | Arkles | 525/92.
|
| 5153238 | Oct., 1992 | Bilgrien et al. | 523/211.
|
| 5322881 | Jun., 1994 | Yamamoto et al. | 524/504.
|
| Foreign Patent Documents |
| 2083014 | May., 1993 | CA.
| |
Other References
R. Buch et al, "Silicone-Based Additives for Thermoplastic Resins Providing
improved Impact Strength, Processing and Fire Retardant Synergy", (Dow
Corning Corp.) - Fire Retardant Chem. Assoc., Oct. 26-29, 1993.
|
Primary Examiner: McCamish; Marion E.
Assistant Examiner: Lee; Helen F.
Attorney, Agent or Firm: Gil; Joseph C., Preis; Aron
Claims
What is claimed is:
1. A thermoplastic molding composition comprising (a) about 75 to 99
percent of a polyamide resin, and (b) about 1 to 25 percent of a silicone
rubber powder, said percent relative to the weight of the composition,
said silicone rubber powder having an average particle size of about 1 to
1000 microns and containing
(i) 100 pbw of a polydiorganosiloxane having a viscosity at 25.degree. C.
is about 10.sup.6 to 10.sup.9 centipoise and siloxane structural units
represented by the general formula
##STR3##
wherein R', R" and R'" independently denote a hydrogen atom, C.sub.1-10
-alkyl, cycloalkyl radicals or aryl groups, and where p is about 1000 to
8000 and where the relative weight proportions of n and m is 98.5 to 100:0
to 1.5, and where
X denotes a member selected from the group consisting of
##STR4##
where R denotes hydrogen, C.sub.1-10 -alkyl, cycloalkyl radicals or aryl
groups and where q is 1-10, and
(ii) about 10 to 80 pbw of a finely divided silica selected from among
fumed silica, precipitated silica and silica gel having a surface area of
at least 50 m.sup.2 /g,
said composition characterized in that it has a notched Izod impact
strength value which is greater than that of the polyamide resin alone.
2. The composition of claim 1 wherein said hydrocarbon radical is selected
from the group consisting of C.sub.1-10 alkyl radicals; alkenyl radicals;
cycloalkyl radicals; and aromatic hydrocarbon radicals.
3. The composition of claim 2 wherein said hydrocarbon radical is a lower
alkyl radical containing 1 to 4 carbon atoms or a phenyl radical.
4. The composition of claim 1 wherein said silica has a surface area of
about 50 to 900 m.sup.2 /g.
5. The composition of claim 1 wherein said p is about 5000 to 6000.
6. The composition of claim 1 wherein the relative weight proportions of n
and m is 99:1.
7. The composition of claim 1 wherein said silica contains sites bonded to
said X.
8. The composition of claim 1 further containing at least one member
selected from the group consisting of a thermal stabilizer, a mold release
agent, a pigment, a flame retarding agent, a uv stabilizer, a hydrolysis
stabilizer, a gamma radiation stabilizer, a plasticizer, a filler and a
reinforcing agent.
9. A thermoplastic molding composition comprising (a) about 85 to 97
percent of a polyamide resin, and (b) about 3 to 15 percent of a silicone
rubber powder, said percent being relative to the weight of the
composition, said silicone rubber powder having an average particle size
of about 1 to 1000 microns and containing
(i) 100 pbw of a polydiorganosiloxane having a viscosity at 25.degree. C.
is about 10.sup.6 to 10.sup.9 centipoise and siloxane structural units
represented by the general formula
##STR5##
wherein R', R" and R'" independently denote a hydrogen atom, C.sub.1-10
-alkyl, cycloalkyl radicals or aryl groups, and where p is about 1000 to
8000 and where the relative weight proportions of n and m is 98.5 to 100:0
to 1.5, and where
X denotes a member selected from the group consisting of
##STR6##
where R denotes hydrogen, C.sub.1-10 -alkyl, cycloalkyl radicals or aryl
groups and where q is 1 to 10, and
(ii) about 20 to 50 pbw of a finely divided silica selected from among
fumed silica, precipitated silica and silica gel having a surface area of
at least 50 m.sup.2 /g,
said composition characterized in that it has a 1/8" notched Izod impact
strength value which is greater than that of the polyamide resin alone.
10. The composition of claim 9 wherein said silica has a surface area of
about 50 to 900 m.sup.2 /g.
11. The composition of claim 9 wherein the relative weight proportions of n
and m is 99:1.
Description
BACKGROUND OF THE INVENTION
The invention concerns thermoplastic molding composition and more
particularly a composition containing a polyamide resin.
The invention is based on the surprising and unexpected finding that the
impact performance of a thermoplastic composition containing a polyamide
resin is improved upon incorporation therewith of a particular silicone
rubber powder. The silicone rubber powder, added at a level of about 1 to
25 percent, relative to the weight of the composition, is characterized in
that it contains a mixture of (a) a polydiorganosiloxane and (b) silica.
The art has long recognized and been concerned with improving the impact
strength of polyamides. A variety of additives have been suggested and
added to polyamides with some improvements being obtained. Many of the
additives are elastomeric, for instance, U.S. Pat. No. 3,668,274 disclosed
improved impact strength by adding a core/shell polymer containing (a) a
core made of a cross linked elastomeric phase and (b) a shell made of a
rigid thermoplastic phase which contains amine-reactive moieties. An
impact resistant polyamide composition containing a graft product of
polybutadiene as a graft substrate and a mixture of acrylate and
acrylonitrile and or acrylamide monomers grafted thereon was disclosed in
U.S. Pat. No. 4,221,879. Also relevant in this context is U.S. Pat. Nos.
4,167,505; 4,174,358 and 4,584,344.
Of particular relevance in the present context is a paper by R. Buch et al
"Silicone-Based Additives for Thermoplastic Resins Providing Improved
Impact Strength, Processing and Fire Retardant Synergy". This prior art
paper (Dow Corning Corporation) disclosed certain silicone powder resin
modifiers products termed RM 4-7081 and RM 4-7051 to be useful in reducing
the rate of heat release and the evolution rates of smoke and carbon
monoxide of burning plastics. Also disclosed is the impact strength
improvement for engineering resins such as polyphenylene ether (PPE) and
PPS. Improved impact strength of polyamides has not been reported.
Also related is Canadian Patent Application 2,083,014 which disclosed the
silicone rubber powder of the present invention as a component in a
composition containing poly(phenylene ether) resin.
It has now been discovered that certain silicone rubber powders, preferably
produced in accordance with the procedure disclosed in U.S. Pat. No.
5,153,238 which is incorporated herein by reference, are useful as impact
modifier in polyamide compositions. The inventive compositions contain
about 1 to 25 percent, preferably 3 to 15 percent relative to the weight
of the composition, of the silicone rubber powder. The improvement to the
impact strength in the context of this invention refers to improvement in
the notched Izod impact strength. Dart impact and unnotched Izod impact
strength were not noted to be favorably changed as a result of the
incorporation of the silicon rubber powder.
The polyamide matrix resin which is suitable for the preparation of the
toughened composition of the present invention is well known in the art
and is readily available in commerce. Embraced within the scope of the
term are semi-crystalline and amorphous polymeric resins having a number
average molecular weight (determined by end-group analysis) of about 5,000
to 30,000 commonly referred to as nylons. Preferably, the molecular weight
is in the range of about 8,000 to 20,000. Suitable polyamides include
those described in U.S. Pat. Nos. 2,071,250; 2,071,251; 2,130,523;
2,130,948; 2,241,322; 2,312,966; 2,513,606; and 3,393,210, the disclosures
of which are incorporated herein by reference. Essentially, the polyamide
resin can be produced by condensation of equimolar amounts of a saturated
dicarboxylic acid containing 4 to 12 carbon atoms with a diamine, in which
the diamine contains 4 to 14 carbon atoms. Excess diamine can be employed
to provide an excess of amine end groups over carboxyl end groups in the
resulting polyamide. Examples of polyamides include polyhexamethylene
adipamide (nylon 66), polyhexamethylene azelamide (nylon 69),
polyhexamethylene sebacamide (nylon 610), polyhexamethylene dodecanoamide
(nylon 612) and bis(paraaminocyclohexyl)methane dodecanoamide. The
polyamide resin can also be produced by ring opening of lactams, for
example polycaprolactam and polylauric lactam, and by condensation of
.omega.-amino carboxylic acids, for example, poly-11-aminoundecanoic acid.
Copolyamides prepared by copolymerization of two or more of the above
polymers or their components, may also be used. The preferred polyamides
are nylon 6, nylon 66, and copolymers of nylon 6 and nylon 66. Preferably
the polyamides are linear and have a melting temperature in excess of
200.degree. C.
The silicone rubber powder of the invention has an average particle size of
about 1 to 1000 microns and contains (i) 100 parts by weight (pbw) of a
polydiorganosiloxane and (ii) about 10 to 80 pbw, preferably about 20 to
50 pbw of a finely divided silica filler.
The polydiorganosiloxane which is characterized in that its viscosity at
25.degree. C. is about 10.sup.6 to 10.sup.9 centipoise is a (co)polymeric
resin having siloxane structural units represented by the general formula
##STR1##
wherein R, R' and R" independently denote hydrogen, C.sub.1-10 -alkyl,
alkenyl, cycloalkyl radicals or aryl groups, and where p is about 1000 to
8000, preferably about 3000 to 6000 and where the relative weight
proportions of n and m are 98.5 to 100:0 to 1.5, preferably 99:1, and
where
X denotes a member selected from the group consisting of
##STR2##
where R denotes hydrogen, C.sub.1-10 -alkyl, alkenyl, cycloalkyl radicals
or aryl groups and where q is 1 to 10.
The organic groups of the polydiorganosiloxane, which may optionally be
halogenated, are preferably lower alkyl radicals containing 1 to 4 carbon
atoms, phenyl and halogen substituted alkyl radicals. Examples include
resins containing dimethylsiloxy units, phenylmethylsiloxy units and
dimethylsiloxy units and diphenyl siloxy units. Most preferably, the
polydiorganosiloxane contains vinyl group(s) or epoxy group(s) at its
chain termination(s) and/or along its main chain. The methods for the
preparation of suitable polydiorganosiloxane are well known; a typical
method comprises the acid- or base-catalyzed polymerization of cyclic
diorganosiloxanes.
The silica filler required in the silicone rubber powder is a finely
divided silica selected from among fumed silica and precipitated silica or
silica gel. These are well known forms of silica and are readily available
in commerce. The suitable silica is characterized in that its surface area
is at least 50 m.sup.2 /g, preferably 50 to 900 m.sup.2 /g.
An additional embodiment entails use of treated silica which contains sites
bonded to groups X as defined above; the manufacture of treated silica,
typically by reacting the silanol groups on the silica surface with about
1 to 2% by weight of an organic alkyl halide compound or an organosilicon
halide compound, is known in the art.
Among the suitable compounds, mention may be made of low molecular weight
liquid hydroxy- or alkoxy-terminated polydiorganosiloxanes,
hexaorganosiloxanes and hexaorganosilazanes.
The procedure for the preparation of the silicone rubber powder has been
described in detail in U.S. Pat. No. 5,153,238, the specification of which
is incorporated herein by reference. Suitable silicone rubber powder is
available in commerce from Dow Corning Corporation under the trademark RM
4-7051 and RM 4-7081.
The preparation of the composition of the invention is carried out
following conventional procedures and by use of conventional means such as
single, preferably twin screw extruders. Conventional thermoplastic
processes are suitable in molding useful articles from the inventive
composition.
Conventional additives may be incorporated in the composition of the
invention in the usual quantities. Mention may be made of a thermal
stabilizer, a mold release agent, a pigment, a flame retarding agent, a uv
stabilizer, a hydrolysis stabilizer, a gamma radiation stabilizer and a
plasticizer for polycarbonate compositions, as well as fillers and
reinforcing agents such as glass fibers.
The invention is further illustrated but is not intended to be limited by
the following examples in which all parts and percentages are by weight
unless otherwise specified.
EXAMPLES
Experimental
Compositions in accordance with the invention have been prepared following
well-known procedures and their properties determined as described below:
the polyamide resin was nylon 6, available from Bayer Corporation as
Durethan B40K resin; the silicone rubber powder was Dow Corning's RM
4-7051. Compositions 2 and 3 show the advantageous impact strength
(notched Izod, 1/8"). All the compositions were produced by extruding in a
twin screw extruder and injection molded (3 oz. Newbury). Since the impact
strength of polyamide is highly dependent on its moisture content, the
impact strength was determined on specimens as molded and on conditioned
samples. The impact strength of the as molded specimens was determined 24
hours after molding; during the 24 hours period, the specimens were held
at 50% relative humidity at 73.degree. F. The notched Izod impact strength
of the conditioned specimens was determined 14 days after molding. During
the 14 days period the specimens were first immersed in deionized water
for seven days at 73.degree. F. and then removed from the water and sealed
in an air tight bag for seven days at 73.degree. F. The impact strength
and moisture absorption of the samples were determined using ASTM D256 and
D570 respectively. A summary of the results is presented below.
Instrumented impact measured as total energy, dart impact, speed of the
dart 15 miles per hour, was determined in accordance with ASTM D 3763. The
unnotched values of the composition showed no advantage for using the
silicon rubber powder.
TABLE 1
______________________________________
Example 1 2 3
______________________________________
Polyamide, wt. % 100 97 90
Silicone rubber powder wt. %
0 3 10
Water Absorption, as molded
1 1 1
Water absorption, conditioned
9 9 9
Dart Impact, ft. lb at 73 F.
8.4 2.7 2.7
Impact strength, ft. lb./in.
notched Izod 1/8"
as molded 1 1.4 2.5
conditioned 1.9 3.2 13.7
______________________________________
Although the invention has been described in detail in the foregoing for
the purpose of illustration, it is to be understood that such detail is
solely for that purpose and that variations can be made therein by those
skilled in the art without departing from the spirit and scope of the
invention except as it may be limited by the claims.
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